Acoustic analysis is a method which today is often used for example in speech recognition however it is rarely ever used in industry application as a condition monitoring technique. The quality of acoustic monitoring is very much dependent on the background noise of the environment, which the machine is operated at. The effect of background noise can be mitigated by sound source localization. Sound source localization might be performed by acoustic camera.
Sound analysis can be an important quality aspect of condition monitoring tool. When faults in machinery and plant installations occur, they can often be detected by a change in their noise emissions. In this way, acoustic camera makes the hearing procedure automated and more objective. Current technologies of acoustic camera can be used to visualize sounds and their sources. Maps of sound sources that look similar to thermo graphic images are created. Noise sources can be localized rapidly and analysed according to various criteria. From U.S. Pat. No. 3,895,340 and U.S. Pat. No. 8,072,839, an acoustic camera consists of some sort of video device, such as a video camera, and a multiple of sound pressure measuring devices, such as microphones, sound pressure is usually measured as Pascal's (Pa). The microphones are normally arranged in a pre-set shape and position with respect to the camera.
The idea of acoustic camera is to do noise/sound source identification, quantification and perform a picture of acoustic environment by array processing of multidimensional acoustic signals received by microphone array and to overlay that acoustic picture to the video picture. It is a device with integrated microphone array and digital video camera, which provides visualization of acoustic environment. Possible applications of acoustic camera as test equipment are nondestructive measurements for noise/sound identification in interior and exterior of vehicles, trains and airplanes, measurement in wind tunnels, etc. Acoustic camera can also be built in complex platform such as underwater unmanned vehicles, robots and robotized platforms etc. When using microphone array consisting of a multiple of microphones, however, it may entail problems regarding the relatively high complexity, a relatively large volume, and a relatively high cost of the acoustic camera.
In some further conventional concepts according to JP Pat. No. 2001.174583, a few microphones are moved between measurements by way of drives, for example motors. The motion tracking of the microphones is done via detection of the parameters of the drives, for example the speed of the motor or the initial position of the motor. The motion of the microphones is limited due to the mechanical restriction of the drive, in other words, the microphone cannot move randomly and some route cannot be followed because of the restriction. Moreover, positional accuracy is limited here in many cases by the length of a sampled or “scanned” area. When moving microphones with motors, the problem of the accuracy of the position of the microphones arises. For example, problems may result due to tolerances of the motor or due to vibrations of the construction. Furthermore, the construction of the arrangement for moving microphones with motors without reflections at fixtures is difficult.